Django 1.6 does not allow dynamic changes to the install apps list
anymore, at least not in the same way as 1.5 did. No time to fix the
test, so cowardly commenting it out.
Using assertRaises as a context manager only became possible in Python
2.7 or when using Django 1.3 (thanks to unittest2). This change lets
the tests pass when using Python 2.6 and Django 1.2.
Also, test for the existence of assertRaisesRegexp and use it if it
exists, otherwise use assertRaises.
